Underground Water
The hydrosphere is the collective mass of water at or near Earth’s surface. Beneath the land surface is the underground water component of the hydrosphere. The total amount of underground water is about 2.5 times greater than that contained in lakes and streams. Moreover, underground water is much more widely distributed than surface water. Whereas lakes and rivers are found only in restricted locations, underground water is almost ubiquitous, occurring beneath the land surface throughout the world. Its quantity is limited in certain areas, its quality is sometimes poor, and its occurrence is sometimes at great depth, but almost anywhere on Earth one can dig deep enough and find water. More than half of the world’s underground water is found within a half mile of the surface. Below that depth the amount of water generally decreases gradually. Although water has been found as deep as six miles underground, at that depth it is almost immobilized because the pressure exerted by overlying rocks is great and openings are few and small.
Almost all underground water comes originally from above. Its source is rain that either percolates (trickles through) directly into the soil or seeps downward eventually from lakes and streams. Once the moisture gets underground, any one of several things can happen to it, depending largely on the nature of the soil and rocks it infiltrates. The quantity of water that can be held in subsurface material (rock or soil) depends on the porosity of the material, which is the total volume of the material that consists of pores or cracks that can fill with water. The more porous a material is, the greater the amount of open space it contains and the more water it can hold.
Porosity is not the only factor affecting underground water flow. If water is to move through rock or soil, the pores must be connected to one another and be large enough for the water to move through them. The ability to transmit underground water (as opposed to just holding it, as in the definition of porosity) is termed permeability, and this property of subsurface matter is determined by the size of the pores and by their degree of interconnectedness. The water moves by twisting and turning through these small, interconnected openings. The smaller and less connected the pore spaces, the less permeable the material and the slower the water moves.
The rate at which water seeps underground depends on both porosity and permeability. For example, clay usually has high porosity because it has a great many openings among the minute flakes that make up the clay, but it generally has low permeability because the openings are so tiny that the force of molecular attraction binds the water to the clay flakes and holds it in place. Thus, clay typically is very porous but relatively impermeable, so it can trap large amounts of water and keep it from draining.
Underground water is stored in, and moves slowly through, moderately to highly permeable rocks called aquifers (from the Latin aqua, water, and ferry, to bear). The rate of movement of water varies with the situation. In some aquifers the flow rate is only a few inches a day; in others, it may be several hundred feet per day. A rapid rate of flow would be 40 to 50 feet per day. In contrast, water can move very slowly or not at all through certain materials. Impermeable materials made up of such elements as clay or very dense rock, which hinder water movement, are called aquicludes.
The general distribution of underground water can probably be best understood by visualizing the layers in a vertical subsurface cross section with at least three and often four hydrologic zones arranged one below another. From top to bottom, these layers are called the zone of aeration, the zone of saturation, the zone of confined water, and the waterless zone.
1
According to paragraph 1, which of the following is true about Earth’s hydrosphere?
AIt is mostly made up of water contained in lakes and rivers.
BIt extends to a depth of at least six miles almost everywhere on Earth.
CIt is spread over wider areas underground than it is at the planet’s surface.
DThe amount of underground water has decreased over long periods of time.
According to paragraph 1, which of the following is true about Earth’s hydrosphere?
AIt is mostly made up of water contained in lakes and rivers.
BIt extends to a depth of at least six miles almost everywhere on Earth.
CIt is spread over wider areas underground than it is at the planet’s surface.
DThe amount of underground water has decreased over long periods of time.
2
The hydrosphere is the collective mass of water at or near Earth’s surface. Beneath the land surface is the underground water component of the hydrosphere. The total amount of underground water is about 2.5 times greater than that contained in lakes and streams. Moreover, underground water is much more widely distributed than surface water. Whereas lakes and rivers are found only in restricted locations, underground water is almost ubiquitous, occurring beneath the land surface throughout the world. Its quantity is limited in certain areas, its quality is sometimes poor, and its occurrence is sometimes at great depth, but almost anywhere on Earth one can dig deep enough and find water. More than half of the world’s underground water is found within a half mile of the surface. Below that depth the amount of water generally decreases gradually. Although water has been found as deep as six miles underground, at that depth it is almost immobilized because the pressure exerted by overlying rocks is great and openings are few and small.
According to paragraph 1, which of the following is true about the deepest underground water that has ever been found?
AIt was found half a mile below the surface.
BIt provides the most abundant supply of water despite being difficult to reach.
CIts movement is limited by pressure from rocks above it.
DIts quality is higher than the quality of water near the surface.
3
Almost all underground water comes originally from above. Its source is rain that either percolates (trickles through) directly into the soil or seeps downward eventually from lakes and streams. Once the moisture gets underground, any one of several things can happen to it, depending largely on the nature of the soil and rocks it infiltrates. The quantity of water that can be held in subsurface material (rock or soil) depends on the porosity of the material, which is the total volume of the material that consists of pores or cracks that can fill with water. The more porous a material is, the greater the amount of open space it contains and the more water it can hold.
All of the following questions about underground water are answered in paragraph 2 EXCEPT
AWhere does it come from?
BHow does it move?
CWhat determines its amount in any given area?
DWhat happens to underground water not held in cracks or pores?
4
Porosity is not the only factor affecting underground water flow. If water is to move through rock or soil, the pores must be connected to one another and be large enough for the water to move through them. The ability to transmit underground water (as opposed to just holding it, as in the definition of porosity) is termed permeability, and this property of subsurface matter is determined by the size of the pores and by their degree of interconnectedness. The water moves by twisting and turning through these small, interconnected openings. The smaller and less connected the pore spaces, the less permeable the material and the slower the water moves.
The phrase this property in the passage refers to
Athe pores beings connected to one another
Bthe ability to transmit underground water
Cthe size of the pores
Dporosity
5
Porosity is not the only factor affecting underground water flow. If water is to move through rock or soil, the pores must be connected to one another and be large enough for the water to move through them. The ability to transmit underground water (as opposed to just holding it, as in the definition of porosity) is termed permeability, and this property of subsurface matter is determined by the size of the pores and by their degree of interconnectedness. The water moves by twisting and turning through these small, interconnected openings. The smaller and less connected the pore spaces, the less permeable the material and the slower the water moves.
According to paragraph 3, the size of the pores in underground material is an important factor in determining
Ahow rapidly water can move through the material
Bhow interconnected the pores in the material are
Chow much water the material can hold
Dhow much the water twists and turns as it moves through the material
6
The rate at which water seeps underground depends on both porosity and permeability. For example, clay usually has high porosity because it has a great many openings among the minute flakes that make up the clay, but it generally has low permeability because the openings are so tiny that the force of molecular attraction binds the water to the clay flakes and holds it in place. Thus, clay typically is very porous but relatively impermeable, so it can trap large amounts of water and keep it from draining.
The word “minute” in the passage is closet in meaning to
Arough
Btiny
Cevenly spaced
Dnumerous
7
The rate at which water seeps underground depends on both porosity and permeability. For example, clay usually has high porosity because it has a great many openings among the minute flakes that make up the clay, but it generally has low permeability because the openings are so tiny that the force of molecular attraction binds the water to the clay flakes and holds it in place. Thus, clay typically is very porous but relatively impermeable, so it can trap large amounts of water and keep it from draining.
In paragraph 4, the author discusses clay in order to show
Ahow permeability is different from porosity
Bhow underground water can sometimes move through materials that are considered impermeable
Cwhy the porosity of underground materials depends on their permeability
Dwhy the attraction among water molecules is generally greater than that among clay molecules
8
The general distribution of underground water can probably be best understood by visualizing the layers in a vertical subsurface cross section with at least three and often four hydrologic zones arranged one below another. From top to bottom, these layers are called the zone of aeration, the zone of saturation, the zone of confined water, and the waterless zone.
The passage implies which of the following about the zone of confined water?
AIt begins about six miles beneath Earth’s surface.
BIt can sometimes appear above the zone of aeration.
CIt is likely to be porous but not permeable.
DIt is unlikely to be made of clay or very dense rock.
9
The hydrosphere is the collective mass of water at or near Earth’s surface. Beneath the land surface is the underground water component of the hydrosphere. [■] The total amount of underground water is about 2.5 times greater than that contained in lakes and streams. [■] Moreover, underground water is much more widely distributed than surface water.[■] Whereas lakes and rivers are found only in restricted locations, underground water is almost ubiquitous, occurring beneath the land surface throughout the world.[■] Its quantity is limited in certain areas, its quality is sometimes poor, and its occurrence is sometimes at great depth, but almost anywhere on Earth one can dig deep enough and find water. More than half of the world’s underground water is found within a half mile of the surface. Below that depth the amount of water generally decreases gradually. Although water has been found as deep as six miles underground, at that depth it is almost immobilized because the pressure exerted by overlying rocks is great and openings are few and small.
Look at the four squaresthat indicate where the following sentence could be added to the passage
This is not to say that underground water is always easy to reach and use.
Where would the sentence best fit？Click on a square sentence to the passage.
10
Much of Earth’s water is located underground.
AThe porosity of rock does not change over time, but its permeability depends on the materials that underground water may contain.
BAlmost all of Earth’s underground water originates from above the planet’s surface and is distributed in hydrologic zones below the surface.
CMost underground water ends up being stored within clay, a highly permeable material found in many regions on Earth.
DUnderground water, which is distributed evenly all over Earth, is found in about equal quantities from just below the surface to 6 miles deep.
EThe porosity and permeability of underground rock affect the quantity of water held in the rock and the water’s movement through it.
FUnderground water moves at widely differing speeds through permeable rocks that are called aquifers.
